US4420226A - Zoom lens of short total length - Google Patents

Zoom lens of short total length Download PDF

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Publication number
US4420226A
US4420226A US06/218,940 US21894080A US4420226A US 4420226 A US4420226 A US 4420226A US 21894080 A US21894080 A US 21894080A US 4420226 A US4420226 A US 4420226A
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sub
lens
lens group
refractive power
component
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English (en)
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Nozomu Kitagishi
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Canon Inc
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Canon Inc
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B15/00—Optical objectives with means for varying the magnification
    • G02B15/14—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
    • G02B15/144—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only
    • G02B15/1441—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only the first group being positive
    • G02B15/144113—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only the first group being positive arranged +-++

Definitions

  • This invention relates to zoom lenses having a zoom ratio of more than three with a telephoto ratio (the total length of the lens system/its focal length) in the longest focal length position reduced to 0.8 or less, and more particularly to a relay lens in the form of the tele type to facilitate the shortening of the total length of the entire system.
  • an increase in a zoom lens' zoom ratio and longest focal length extends its mechanical length and significantly diminishes its portability and manageability.
  • photographic lenses with medium to long focal lengths in the telephoto positions when used in sports photography, animal, bird, and other wildlife photography, are handheld while shooting. Because this requires rapid and easy handling of the camera associated therewith, as well as of the lens, it is essential that the lens be compact.
  • a zoom lens having a wide range and constructed to shorten its total length is disclosed, for example, in Japanese Patent Application Publication No. Sho 49-24295. However, this lens is as slow as F/8.
  • An object of the present invention is to meet the aforementioned needs and to provide a zoom lens with high grade imaging performance and an increased zoom ratio while maintaining its compactness.
  • the present invention contemplates the use of, in particular, method (3), that is, of configuring the relay lens to be a strong tele type with the resultant distance from the front vertex of the relay lens to the focal plane of the complete lens being shortened, thus shortening the total length of the entire system.
  • the employment of the tele type for use in the relay lens for shortening of the total length gives rise to an alternate disadvantage that as the Petzval sum increases in the negative sense, extreme over-correction of field curvature results and the coma and astigmatism deteriorate. It is, therefore, an object of the present invention to provide a zoom lens having a greatly shortened total length while nevertheless preventing deterioration of the above-described aberrations.
  • the relay lens is so configured and is characterized by satisfying the conditions in the claims, and as exemplified in the detail disclosure to follow.
  • FIG. 1 is a lens diagram of Example 1 embodying the invention.
  • FIGS. 2(a) to (c), 3(a) to (c) and 4(a) to (c) are graphic representations of the various aberrations of the zoom lens of FIG. 1 when in the wide angle, middle and telephoto settings respectively.
  • FIG. 5 is a lens diagram of Example 2 of the invention.
  • FIGS. 6(a) to (c), 7(a) to (c) and 8(a) to (c) are graphic representations of the aberrations of the lens of FIG. 5 in the wide angle, middle and telephoto settings respectively.
  • FIG. 9 is a lens block diagram of Example 3 the invention.
  • FIGS. 10(a) to (c), 11(a) to (c) and 12(a) to (c) are graphic representations of the aberrations of the lens of FIG. 9 in the wide angle, middle and telephoto settings respectively.
  • FIG. 13 is a lens diagram of Example 4 embodying the invention.
  • FIGS. 14( a) to (c), 15(a) to (c) and 16(a) to (c ) are graphic representations of the aberrations of the lens of FIG. 13 in the wide angle, middle and telephoto settings respectively.
  • FIG. 17 is a lens diagram of Example 5 embodying the invention.
  • FIGS. 18(a) to (c), 19(a) to (c) and 20(a) to (c) are graphic representations of the aberrations of the lens of FIG. 17 in the wide angle, middle and telephoto settings respectively.
  • FIG. 21 is a lens diagram of Example 6 embodying the invention.
  • FIGS. 22(a) to (c), 23(a) to (c) and 24(a) to (c) are graphic representations of the aberrations of the lens of FIG. 21 in the wide angle, middle and telephoto settings respectively.
  • the zoom lens of the present invention has as its general configuration an almost afocal section consisting of a convergent first lens group I axially movable for focusing, a divergent second lens group II axially movable for zooming, and a convergent third lens group II axially movable for the image shift compensation followed by an image forming rear lens group or fourth lens group IV which is stationary during zooming.
  • the convergent rear lens group IV comprises, from front to rear, first lens component consisting of a positive singlet with its front surface of strong curvature convex toward the front, a second lens component consisting of a meniscus doublet of forward convexity positioned adjacent the first component and having a weak refractive power with its cemented surface convex toward the front, a third lens component consisting of a positive singlet positioned in a large air separation from the above-described second component, and a fourth lens component consisting of a meniscus doublet of forward concavity positioned adjacent the third component, said rear section satisfying at least one of the following conditions:
  • F R is the focal length of the rear section
  • F I ,II is the overall focal length of the first and second components in the rear lens group
  • ⁇ II is the refractive power of the second component in the rear lens group.
  • r R .sbsb.4 is the radius of curvature of the cemented surface in the second component in the rear lens group.
  • n Ri is the index of refraction of the material of the i-th lens element counting from the front in the rear section.
  • Condition (1) serves to shorten the distance from the front vertex of the 4th lens group to the focal plane of the entire system.
  • the front assembly of the rear section (which consists of the first and second components) includes a strong positive lens group having a focal length equal to 0.65 to 0.71 times the focal length of the fourth lens group.
  • the relay lens is configured into an extremely strong tele type lens.
  • the rear assembly (which consists of the third and fourth components of the fourth lens group) includes a negative lens group in which the absolute focal length is equal to 0.93 to 1.18 times the focal length of the fourth lens group with a large air separation from the front assembly.
  • the zoom lens of the invention With a relay section of a shorter overall length.
  • the focal length of the front group of the relay lens is longer than the upper limit of condition (1), the total length of the complete zoom lens cannot be greatly shortened.
  • the lower limit is exceeded, the total length can be advantageously shortened, but it becomes difficult to compensate for the over-corrected field curvature even when conditions (2) to (5) are satisfied. Correction of astigmatism and coma also becomes difficult.
  • Conditions (2) to (5) are to correct the aberrations in the strong tele type relay lens.
  • the refractive power of the second component of the fourth lens group is stronger than the upper limit of condition (2), though the total length is shortened, spherical aberration is under-corrected and this cannot be compensated for.
  • the refractive power of the second component of the fourth lens group is stronger in negative sense than the lower limit, the overall refractive power of the front assembly of the relay lens becomes so weak that shortening of the total length is no longer achieved.
  • the second component of the fourth lens group is then provided with a cemented surface convex toward the front and exhibits the strong curvature defined in condition (3) and, more preferably, possesses the refractive index difference in the lens elements on the both sides of the cemented surface defined by condition (4) to correct for field curvature while preventing the other aberration from deteriorating.
  • the configuration of the cemented surface to the forward convexity which constitutes one of the features of the invention serves to prevent the converging rays of light incident upon the cemented surface from being steeply refracted. Hence, the lateral aberration produced by that surface is minimized.
  • the over-corrected field curvature can be advantageously compensated for, but instead the higher order spherical aberration and coma, in particular, that portion of the coma which is ascribable to the marginal rays of light in relation to the center of the area of diaphragm aperture, are increased objectionably.
  • the radius of curvature of the cemented surface in the second component of the fourth lens group is larger than the upper limit of condition (3), it becomes impossible to compensate for the over-corrected field curvature.
  • Inequality (4) provides a similar condition to that of inequality (3) in that the over-corrected field curvature is compensated for.
  • the zoom lens of the invention includes the second component of the fourth lens group in the form of the cemented lens with the main aim of improving of field curvature. That is, the Petzval sum which would be otherwise increased in the negative sense is intended to assume a minimum value.
  • the second component of the fourth lens group lacks the cemented surface, or if the doublet in the embodiment to be described later were replaced by a singlet having a refractive index equal to the mean refractive index of the doublet, the Petzval sum would reach a value as large as -0.11.
  • the introduction of the cemented surface defined by conditions (3) and (4) into the second component of the fourth lens group as in the embodiment of the invention results in the reduction of the Petzval sum to a value as small as -0.033. It will be appreciated that the residual curvature of field is well corrected for. When the lower limit of inequality (4) is exceeded, it becomes difficult to compensate for the over-corrected curvature of field. On the other hand, when the upper limit is exceeded, higher order spherical aberrations are produced.
  • Inequality (5) represents a condition for compensation of spherical aberration and curvature of field. That is, when the lower limit is exceeded, it becomes difficult to achieve the compensation for the spherical aberration. When the upper limit is exceeded, the satisfaction of the conditions defined by the inequalities (2), (3) and (4) does not lead to sufficient compensation for the over-corrected curvature of field.
  • the total length of a zoom lens is remarkably shortened as compared to known zoom lenses of the same general configuration mentioned above by the use of the relay section of the strong tele type defined by inequality (1) and is well corrected for the Petzval sum and spherical aberration by satisfying at least one of the conditions (2) to (5) throughout the extended range of variation of the focal length.
  • the present invention offers the advantage of providing a zoom lens of greatly extended range with remarkably shortened total length, and which lens is well corrected for high grade imaging performance over the entire zooming range.
  • a number of examples of specific zoom lenses can be constructed as represented by the numerical values given in the following tables for the radii of curvature R, the lens thicknesses and air separations D, the Abbe numbers ⁇ for the various lens elements, the corresponding indices of refraction Nd, spherical aberration coefficients SA, coma coefficients CM, astigmatism coefficients AS, distortion coefficients DS and Petzval sums PT.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Lenses (AREA)
US06/218,940 1979-12-28 1980-12-22 Zoom lens of short total length Expired - Lifetime US4420226A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP17134279A JPS5695212A (en) 1979-12-28 1979-12-28 Zoom lens of short overall length
JP54-171342 1979-12-28

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US4420226A true US4420226A (en) 1983-12-13

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4468098A (en) * 1981-10-06 1984-08-28 Asahi Kogaku Kogyo Kabushiki Kaisha Compact telephoto zoom lens system
US4789226A (en) * 1983-07-22 1988-12-06 Olympus Optical Co., Ltd. Zoom lens system
US5680249A (en) * 1994-08-23 1997-10-21 Asahi Kogaku Kogyo Kabushiki Kaisha Optical system for camera

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2506744B2 (ja) * 1987-04-07 1996-06-12 松下電器産業株式会社 ズ−ムレンズ
JPS6479719A (en) * 1987-09-21 1989-03-24 Asahi Optical Co Ltd Telephoto zoom lens
JP2529373B2 (ja) * 1988-12-21 1996-08-28 松下電器産業株式会社 ズ―ムレンズ

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE28591E (en) 1970-12-24 1975-10-28 Optical system for the magnification varying portion of an ultra-telephoto type zoom lens
US4145115A (en) * 1977-03-23 1979-03-20 Vivitar Corporation Zoom lens
US4307943A (en) * 1978-09-11 1981-12-29 Vivitar Corporation Close focusing zoom lens

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE28591E (en) 1970-12-24 1975-10-28 Optical system for the magnification varying portion of an ultra-telephoto type zoom lens
US4145115A (en) * 1977-03-23 1979-03-20 Vivitar Corporation Zoom lens
US4307943A (en) * 1978-09-11 1981-12-29 Vivitar Corporation Close focusing zoom lens

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4468098A (en) * 1981-10-06 1984-08-28 Asahi Kogaku Kogyo Kabushiki Kaisha Compact telephoto zoom lens system
US4789226A (en) * 1983-07-22 1988-12-06 Olympus Optical Co., Ltd. Zoom lens system
US5680249A (en) * 1994-08-23 1997-10-21 Asahi Kogaku Kogyo Kabushiki Kaisha Optical system for camera

Also Published As

Publication number Publication date
JPS5695212A (en) 1981-08-01
JPS6145809B2 (enrdf_load_stackoverflow) 1986-10-09

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